Bentonite clay has proved to be useful where a swelling agent is necessary or desired since, as is well known, one property of such clay is to swell in the presence of moisture.
Bentonite clay is an essential ingredient of drilling muds in petroleum production. At the present time, bentonite clay is in short supply because of the increase in drilling activity due to the energy crisis and the extensive use of this clay in moulding sands. While bentonite clay from the upper horizons of a geological deposit is often quickly usable, it has been heretofore customary to beneficiate bentonite clay from the lower horizons of a geological deposit by spreading it out on the surface of the ground and allowing it to "weather" for at least a year to improve the product quality. However, in order to meet the demand of the petroleum industry, the poorer quality bentonite clay from the lower horizons of the deposit has sometimes been mixed, without the benefit of weathering, with the bentonite clay from the upper horizons of the deposit to thereby reduce the over-all quality of the product.